The present invention relates to novel cross-linking agents (xe2x80x9ccross-linkersxe2x80x9d) for negative photoresist compositions usable in the deep ultraviolet region of the light spectrum, a process for preparing the same, and negative photoresist composition using the same. More specifically, it relates to cross-linkers for photoresists which are suitable for photolithography processes using KrF (248 nm), ArF (193 nm), E-beam, ion beam or EUV light sources when preparing a microcircuit of a highly integrated semiconductor element, and photoresist compositions employing the same.
Recently, chemical amplification type DUV (deep ultra violet) photoresists have proven to be useful to achieve high sensitivity in processes for preparing micro-circuits in the manufacture of semiconductors. These photoresists are prepared by blending a photoacid generator with polymer matrix macromolecules having acid labile structures.
According to the reaction mechanism of such a photoresist, the photoacid generator generates acid when it is irradiated by ultraviolet rays from the light source, and the main chain or branched chain of the polymer matrix macromolecule is cross-linked with the generated acid to form a cross-linked structure. Thus, the portion exposed to light cannot be dissolved by developing solution and remains unchanged, thereby producing a negative image of a mask on the substrate. In the lithography process, resolution depends upon the wavelength of the light sourcexe2x80x94the shorter the wavelength, the smaller the pattern that can be formed. However, when the wavelength of the light source is decreased in order to form a micro pattern [for example, in the case of using 193 nm wavelength or EUV (extremely ultraviolet) light], it is disadvantageous in that the lens of the exposing device is deformed by the light source, thereby shortening its life.
Melamine, a conventional cross-linker, has only three functional groups to cross-link with acid. Further, a large amount of acid must be generated when melamine is used as a cross-linker, because acid is consumed by the cross-linking reaction. As a result, higher energy light-exposure is required for such cross-linking agents.
In order to overcome the disadvantages described above, chemical amplification type components that cross-link with a photoresist resin and use less amounts of energy are desired. However, such chemical amplification type cross-linkers have not yet been developed.
Furthermore, in a pattern of high integrity, developing solution may be soaked into the cross-linked site, to swell up the cross-linked site. Thus, in order to form a pattern of higher integrity, the incorporation of a novel cross-linker, which performs cross-linking more elaborately, is required.
FIG. 1 shows a photoresist pattern that was formed by using a photoresist composition comprising a conventional cross-linker (J. Photopolymer Science and Technology, Vol.11, No.3, 1998, 507-512). The pattern is a 0.225 xcexcm L/S pattern obtained by a photolithography process employing an ArF light source and a monomeric cross-linker.
As can be shown from FIG. 1, swelling occurs in a conventional photoresist pattern, so that a pattern of less than 0.225 xcexcm L/S is difficult to obtain.
The object of the present invention is to provide a photoresist cross-linker, and a process for preparing the same.
Another object of the present invention is to provide a photoresist composition comprising the cross-linker, and a process for preparing the composition.
Still another object of the invention is to provide a semiconductor element manufactured by using the photoresist composition.
In order to achieve these objects, the present invention provides a cross-linker monomer that comprises a compound represented by following Chemical Formula 1:
 less than Chemical Formula 1 greater than 
wherein, R1, R2 and R individually represent straight or branched C1-10 alkyl, straight or branched C1-10 ester, straight or branched C1-10 ketone, straight or branched C1-10 carboxylic acid, straight or branched C1-10 acetal, straight or branched C1-10 alkyl including at least one hydroxyl group, straight or branched C1-10 ester including at least one hydroxyl group, straight or branched C1-10ketone including at least one hydroxyl group, straight or branched C1-10 carboxylic acid including at least one hydroxyl group, and straight or branched C1-10 acetal including at least one hydroxyl group; R3 represents hydrogen or methyl; m represents 0 or 1; and n represents a number of 1 to 5.
In order to achieve another object of the present invention, a photoresist composition is provided which comprises (i) a photoresist polymer, (ii) a photoresist cross-linker as described above, (iii) a photoacid generator and (iv) an organic solvent.